We achieved a pressure of 52.1 gigapascals with moissanite anvils, which have optical, thermal, electric, magnetic, and x-ray properties that rival those of diamond. The mode-softening of D 2 O toward the pressure-induced hydrogen bond symmetrization and the Raman shifts of diamond under hydrostatic and nonhydrostatic compressions were studied with moissanite anvils in the spectral regions normally obscured by diamond anvils. Moissanite anvil cells allow maximum sample volumes 1000 times larger than those allowed by diamond anvil cells and may enable the next level of advancement in high-pressure experiments.

https://science.sciencemag.org/content/sci/290/5492/783.full.pdf

Moissanite: A Window for High-Pressure Experiments

Copper oxide superconductors possess multi-layered structures with a layer sequence of -CuO2 -(Q-CuO2 )n -1 -AO-(MO1± )m -AO- or -CuO2 -B-(O2 -B)s -1 -CuO2 -AO-(MO1± )m -AO- along the elongated c axis. Based on this layer sequence, the known copper oxide structures are categorized as members of the homologous series, Mm Ar Qn -1 Cun Om +r +2n ± (M-mr (n -1)n ; category A) or Mm A2k Bs Cu1+k Om +4k +2s ± (M-m (2k )s (1+k ); category B). Stabilization of such structures especially in the case of high values of the n /s parameter, i.e. the higher members of the homologous series, has been demonstrated to be apparently promoted under high pressures and/or strongly oxidizing conditions. Consequently, techniques for applying both high oxygen gas pressures (10-2000 atm) and ultra-high solid-medium pressures (2-8 GPa) have been advantageously utilized in synthesizing various superconductive copper oxide phases. Especially the ultra-high solid-medium pressure synthesis carried out in the so-called cubic-anvil/belt-type apparatus has proven to be extremely successful in synthesizing novel superconductive phases. In order to achieve high partial pressures of oxygen in the solid-medium environment, `external' oxygen-generating oxides such as KClO4 , KClO3 and Ag2 O2 are commonly added to the precursor mixtures. It is emphasized that in some cases it is possible to utilize `internal' oxidizing agents alone, i.e. highly oxidized precursors such as BaCuO2+ and Ba2 Cu3 O5+ containing metal constituents common with the desired copper oxide phase only. In the present paper, the potential and applications of high-pressure techniques in synthesizing multi-layered copper oxides and related structures are reviewed and discussed with emphasis on the important `historical' discoveries of novel phases and the present status of controlled production of high-quality samples of such phases.

https://iopscience.iop.org/article/10.1088/0953-2048/13/4/202/pdf

Application of high-pressure techniques: stabilization and oxidation-state control of novel superconductive and related multi-layered copper oxides

The ZnSe powder and ${\mathrm{Zn}}_{0.84}$${\mathrm{Fe}}_{0.16}$Se crystal were studied by Raman scattering spectroscopy at pressures up to 36.0 and 32.0 GPa, respectively. For ZnSe powder at 4.7 and 9.1 GPa, two phase transitions were observed. However, the resulted phases have not been identified yet. As the pressure was increased to 14.4 GPa, the LO phonon peak disappeared while the TO phonon peak was still visible until the metallization pressure, 17.0 GPa was reached. In addition, three unidentified Raman peaks were still observable above the metallization pressure. For ${\mathrm{Zn}}_{0.84}$${\mathrm{Fe}}_{0.16}$Se crystal, the structure transition from possible zinc blende to sodium chloride phase (${\mathrm{B}}_{1}$) was identified by the disappearance of Fe local mode and longitudinal optical (LO) phonon mode at 10.9 GPa. In addition, an unidentified phase transition at 4.7 GPa was observed. The TO phonon and the split TO phonons were still observable at a pressure above the phase transition pressure up to 32.0 GPa. The existence of Fe impurity in the ZnSe up to a concentration of 0.16 reduced the semiconductor-metal phase transition pressure to 10.9 GPa. According to the calculation of Gr\"uneisen parameters, ${\mathrm{Zn}}_{0.84}$${\mathrm{Fe}}_{0.16}$ Se was found to have a higher ionicity than ZnSe. Reasons for the observation of Raman peaks at a pressure above the metallization pressure are still unknown.

Raman spectroscopy study of ZnSe and Zn 0.84 Fe 0.16 Se at high pressures

Use of high-quality single-crystal moissanite as anvils has made possible a versatile high-pressure apparatus complementary to the diamond anvil cell (DAC) for high-pressure studies to at least the half-megabar pressure range. High-pressure research has been revolutionized by the DACs as a result of the great strength and transparency of diamond. However, the technique often suffers from interference by the diamond spectra and is limited by small anvil sizes. Other gem anvils, such as sapphire and cubic zirconia, have not been able to reach beyond 26 GPa. With gem-quality synthetic moissanite as anvils, we pressurized samples to close to 60 GPa. Moissanite anvils can be made two to three orders of magnitude larger than conventional diamonds, thus providing new opportunities for studies of material properties at high pressures with analytical techniques that are limited to small samples.

https://iopscience.iop.org/article/10.1088/0953-8984/14/44/513/pdf

The moissanite anvil cell: a new tool for high-pressure research

We propose a new Raman pressure scale based on the shift with pressure of the fundamental Raman band of micrometer-sized diamonds. First, we confirmed that the pressure slope of the triply degenerate diamond phonon behaves in a similar fashion to that of the bulk. Our measurements were calibrated Raman against the Sm:YAG fluorescence pressure scale up to 5 GPa using a gasketed sapphire anvil cell. The most relevant features regarding the design of the anvil cell are briefly outlined. Measurements were performed under hydrostatic conditions using 4 : 1 methanol–ethanol as pressure-transmitting medium. The calibration pressures according to the relationship p(GPa) = 0.356[ν(cm−1) − 1332.3] are considered to be accurate within about 0.1 GPa. The convenience of using micrometer-sized diamonds as pressure sensors in Raman studies using gem anvil devices is demonstrated with several examples. Copyright © 2003 John Wiley & Sons, Ltd.

Diamond as pressure sensor in high‐pressure Raman spectroscopy using sapphire and other gem anvil cells

In analogy with the bevelled diamonds in diamond anvil cells, some transparent gems are used as anvils for generating static ultrahigh pressure. The maximum pressure within which these gem anvil cells could generale was 16.7 GPa in cubic-zirconia anvil cell and 25.8 GPa in sapphire anvil cells, respectively.

Ultrahigh pressures in gem anvil cells

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Ultrahigh pressures in gem anvil cells